Polymeric substrates are becoming more important in the manufacture of ink-receiving elements for ink-jet printing (e.g. resin coated paper, polyesterfilm, etc). One of the applications of ink-jet recording elements on a polymeric substrate for ink-jet printing is the production of transparencies. These elements are primarily intended for use on an overhead projector. More generally, these elements can be used for all kinds of viewing means by transmitted light. Such a transparency for overhead projection can easily be created by applying liquid ink dots to the ink-receptive layer using equipment such as ink jet printers.
In the ink jet printing technique the individual ink droplets can be applied to the receiving substrate in several different ways. The ink solution can be jetted continuously through a small nozzle towards the receiving layer (Hertz method). The ink droplet can also be created "upon demand" by a piezoelectric transducer or a thermal push (Bubble Jet).
It is known that the ink-receptive layers in transparent ink-jet recording elements must meet different stringent requirements:
The ink-receiving layer should have a high ink absorbing capacity, so that the dots will not flow out and will not be expanded more than is necessary to abtain a high optical density, even if ink droplet in a multi-color system may be superposed on the same physical spot. PA1 The ink-receiving layer should have a high ink absorbing speed (short ink drying time) so that the ink droplets will not feather if smeared immediately after applying. PA1 The ink-receiving layer should be excellent in color forming characteristics. PA1 The ink dots that are applied to the ink-receiving layer should be smooth at their peripheries and have a shape of a true sphere. The dot diameter must be constant and accurately controlled. PA1 The ink-receiving layer must be readily wetted so that there is no "puddling", i.e. coalescence of adjacent ink dots, and an earlier absorbed ink drop should not show any "bleeding", i.e. overlap with neighbouring or later placed dots. PA1 The ink-jet recording element must have a low haze-value and be excellent in transmittance properties. PA1 After being printed the image must have a good resistance regarding waterfastness, lightfastness and indoor-discoloration. PA1 The ink-jet recording element may not show any curl or sticky behaviour if stacked before or after being printed. PA1 i. binary blends comprised of from about 10 to about 90 percent by weight of polyethylene oxide or gelatine and from about 90 to about 10 percent by weight of an other component selected from the group mentionned above. PA1 ii. ternary blends comprised of from about 10 to about 50 percent by weight of polyethylene oxide from about 85 to about 5 percent by weight of sodium carboxymethyl cellulose and from about 5 to about 45 percent by weight of an other component selected from the group mentionned above. PA1 iii. ternary blends comprising of from about 10 to about 50 percent by weight of gelatin, from about 85 to about 5 percent by weight of sodium carboxymethyl cellulose and from about 5 to about 45 percent by weight of a component selected from the group mentionned above. PA1 iv. ternary blends comprised of from about 10 to about 50 percent by weight of gelatin, from about 85 to about 5 percent by weight of polyvinyl pyrrolidone and from about 5 to about 45 percent by weight of an other component selected from the group mentionned above. PA1 hydroxyethylmethyl cellulose, 75 percent by weight, and polyethylene oxide, 25 percent by weight; PA1 gelatin, 80 percent by weight and polyethylene oxide, 20 percent by weight; PA1 gelatin, 70 percent by weight, and polyvinyl pyrrolidone, 30 percent by weight; PA1 gelatin, 80 percent by weight, and polyvinylalcohol, 20 percent by weight; PA1 sodium carboxymethyl cellulose, 80 percent by weight, and gelatin, 20 percent by weight. PA1 gelatin, 50 percent by weight, sodium carboxymethyl cellulose, 25 percent by weight, and polyethylene oxide, 25 percent by weight; PA1 gelatin, 60 percent by weight, polyvinyl pyrrolidone, 20 percent by weight, and polyvinyl alcohol, 20 percent by weight; PA1 gelatin, 50 percent by weight, polyvinyl pyrrolidone, 25 percent by weight, and sodium carboxymethyl cellulose, 25 percent by weight. PA1 F(CF.sub.2).sub.4-9 CH.sub.2 CH.sub.2 SCH.sub.2 CH.sub.2 N.sup.+ R.sub.3 X.sup.- wherein R is an hydrogen or an alkyl-group; and in U.S. Pat. No. 5,084,340, having a structure of: CF.sub.3 (CF.sub.2).sub.m CH.sub.2 CH.sub.2 O(CH.sub.2 CH.sub.2 O).sub.n R wherein m=2 to 10; n=1 to 18; R is hydrogen or an alkyl group of 1 to 10 carbon atoms. These surfactants are commercially available from DuPont and 3M. The concentration of the surfactant component in the ink-receptive layer is typically in the range of 0.1 to 2 percent, preferably in the range of 0.4 to 1.5 percent and is most preferably 0.75 percent by weight based on the total dry weight of the layer.
To meet these requirements, the ink receptive layers of the prior art have been prepared for a long time using many different materials. A dimensionally stable substrate such as polyethyleneterephtalate (PET), cellulosetriacetate, or paper is used most frequently and coated with one or more polymer coatings. These receiving polymer coatings comprise one or more binders and different additives which are necessary to meet the requirements mentioned above.
In the German Patent Application DE 2,234,823 an ink receiving layer comprising gelatin and different particulates and colour molecules is described. U.S. Pat. No. 3,889,270 describes an ink-receiving layer comprising a molecular or colloidal disperse phase that enables the jetting ink to penetrate a few microns into this layer. The binder (gelatin, albumin, casein, proteins, polysaccharide, cellulose and its derivatives, (copolymers of) polyvinylalcohol is combined with hydrophylic silica and a white toner.
U.S. Pat. No. 4,503,111 describes an ink-receiving layer where a first binder (gelatin or polyvinylalcohol (PVA)) is mixed with a polyvinylpyrrolidone (PVP) having a molecular weight of at least 90000, and for which the ratio PVA/PVP is in the range 3:1 to 1:3.
This mixture of PVA, PVP or copolymers can also be combined with a coalesced latex of co-PVA-Polyvinyl-benzylammoniumchloride (U.S. Pat. No. 4,547,405) yielding a further improvement in waterfastness.
An additional improvement in maximum density and drying time can be obtained using particulates in the binder. Many patent applications have described this effect for many different binder-systems. U.S. Pat. No. 3,357,846 describes pigments such as kaolin, talc, bariet, TiO2 used in starch and PVA. U.S. Pat. No. 3,889,270 describes silica in gelatin, PVA and cellulose. Pigments and particles have also been described in patent applications DE 2,925,769, GB 2,050,866, U.S. Pat. No. 4,474,850, U.S. Pat. No. 4,547,405, U.S. Pat. No. 4,578,285, WO 88 06532, U.S. Pat. No. 4,849,286, EP 339 604, EP 400 681, EP 407 881, EP 411 638 and US 5,045,864.
In many patent applications the tuning of the surface energy and polarity of the receiving layer is done by the use of special (fluoro) tensides: e.g. U.S. Pat. No. 4,578,285, U.S. Pat. No. 4,781,985 and U.S. Pat. No. 5,045,864.
The drying time characteristic can also be improved by a better tuning of the pH value of the coating solution, as described in unpublished European Application 92 203316.2
An improvement in waterfastness is mostly realised by the use of ammonium mordanting polymers. These polymers interact with most typical ink jet inks resulting in a better localisation of the dye in the binder. Typical examples of such descriptions are U.S. Pat. Nos. 4,371,582, 4,575,465, 4,649,064, GB 2,210,071 and EP 423 829. For instance in U.S. Pat. No. 4,371,582 a basic polymer latex comprising tertamino- or quaternary ammonium groups is described. In U.S. Pat. No. 4,575,465 an ink-receiving layer comprising a hydrophilic polymer with up to 50% by weight of vinylpyridine/vinylbenzylquaternary ammonium salt copolymers is claimed. In U.S. Pat. No. 4,649,064 the quaternary ammonium derivatives are used in combination with calciumacetate, a binder, a suitable crosslinker for the binder, and an ink composition comprising a binder and a crosslinkable dye.
Unfortunately, these transparent ink-jet recording elements with ink-receiving layers that have been described in the prior art fail to combine a short drying time with an excellent waterfastness, especially when the layers are printed with conventional non reactive, water based inks.